An ongoing objective in watercraft hull design has been to minimize water-induced drag on the hull as it is propelled through the water, thereby effecting faster speeds and less fuel consumption. Three types of watercraft have been traditionally utilized with varying degrees of success to achieve the above objectives, the three types being displacement crafts, hydrofoil craft and planing craft. The displacement craft forms a wave at the bow of the boat which, at slow speeds has a single crest. As the speed of the craft increases, a second crest is formed which moves rearwardly, ultimately causing the craft to sink when a certain maximum speed is reached. The planing watercraft does not have this disadvantage because its hull is designed so that as the speed of the craft increases, it is lifted to and planes across the surface of the water. However, a great amount of power is required to bring the craft to planing speed, and relatively small waves at the water surface tend to capsize the craft. Thus planing vessels are dangerous to operate and primarily limited to racing events. The hyrofoil craft utilizes hydrofoils which are attached to the sides of the vessel and extend downwardly into the water below the lowermost portion of the hull of the craft. As the hydrofoil craft initially moves forward, the hull acts as that of a displacement craft. However, as its speed increases, the hydrofoils tend to lift the craft so that the hull no longer contacts the water, thereby resulting in the reduced water drag experienced by the planing craft. Hydrofoil craft exhibit considerably more stability than planing craft. All of the above watercraft have some disadvantages. The displacement craft is limited to relatively low speeds and has a maximum speed beyond which it will capsize. The planing craft can achieve high speeds, but is dangerous to operate. The hydrofoil craft, although overcoming some of the disadvantages of the displacement and planing craft, requires a specialized hull which is expensive to produce and is somewhat limited to use in larger craft.
The present invention discloses aerodynamic lift means which can be attached to either an inboard or outboard displacement type boat, preferably a water ski boat, thereby increasing its speed without the danger associated with a planing craft. The lift means acts through both the front portion and rear portion of the boat, thereby raising both the front and rear portions as the boat is propelled through the water. Such an arrangement has been disclosed and claimed in my copending application Ser. No. 890,746, filed Mar. 27, 1978, entitled "Winged Ski Boat". In the present embodiment, the lift means acting on the rear portion of the boat includes vertical stabilization fins, each having a portion canted to an angle of at least 30.degree., preferably in the range of 30.degree.-40.degree. from vertical. The canted fins serve to provide lateral stability and to concentrate forces acting on the boat to the middle of the boat. By raising both portions of the boat in this manner, some of the disadvantages of displacement type craft are overcome since the amount of hull surface area in contact with the water is reduced while at the same time the boat is stabilized. This is effected without the large power requirements and inherent danger associated with a planing craft or the unique hull design required by a hydrofoil craft.
In a specific embodiment, an outboard water ski boat is configured with a wing removably attached to the front portion of the boat and a pair of stacked wings removably attached to the rear portion of the boat. The angle of attack of each wing can be independently adjusted, thereby providing a lift adjustment means. Vertical stabilization fins are provided for the ends of the aft wings and can be provided for the ends of the front wings, the fins providing increased lateral stability for the boat. As above described, the rear vertical fins are each formed with a portion canted, inwardly or outwardly, to at least 30.degree., preferably in the range of 30.degree.-40.degree. from vertical, exemplified in the Figures by 35.degree.. A ski boat configured according to the invention has a smoother ride in that the boat rides higher on the water surface as it is propelled forward, yet remains stable. This additional height, and associated drag reduction, allows the ski boat to go faster with a given power source. In a specific model utilizing an 18 foot boat, the speed was increased from 60 m.p.h. without the lift producing wings to between 75 m.p.h. and 80 m.p.h. with the lift producing wings. Less fuel is used to maintain a predetermined speed because there is less drag created between the water and the hull surface extending into the water. Another advantage of the invention is that it allows a larger propeller to be used in conjunction with a given propulsion means because the rear portion of the boat is higher in the water than it would be without the wings, thereby lifting a portion of the propeller out of the water and reducing propeller drag.